1. Field of the invention:
This invention relates to a method for closing the opening of each of the through-holes formed in the pipe-wall of a resin pipe and extending parallel to the axis of said pipe.
2. Description of the prior art:
In order to reduce the weight of a pipe and the amount of materials used in a pipe, and to provide a pipe with improved strength against a flattening load so as to minimize deformation due to stress caused by an earth load, etc., attempts have been made by forming a multiplicity of axially extending through-holes 13 in spaced parallel relation in the pipe-wall of a resin pipe, for example, as shown in FIG. 1. Such a resin pipe 1 is used for buried sewage piping, etc., since it has considerably high flattening rigidity characteristics. The usual method for connecting such resin pipes 1 is to insert a diametrically enlarged end (socket side) of a pipe into a diametrically nonenlarged end (spigot side) of another pipe, and then to join the pipes together by applying an adhesive or by attaching a seal ring. However, such method has a disadvantage in that the through-holes 13 formed in the pipe-wall of the pipe communicate with various parts within and/or outside of the piping, whereby fluid leakage from the piping or inflow of underground water into the piping may occur. Accordingly, such pipes cannot be used as is. It is necessary to close the through-holes 13 on the socket side or spigot side after extrusion molding or secondary processing of the pipe.
In Japanese Published Examined Patent Application No. 57-44111, as FIGS. 1 and 10 illustrate, it was proposed to place a heated pipe end 10 in a mold 103, then press the pipe end 1 0 against the mold 103 while rotating the mold 103, whereby the hole-partition walls 130 are twisted. By twisting the pipe end 10 in this way, the inner and outer walls 11, 12 thereof are pressed together, thereby closing the through-holes 13. However, the portion subjected to such treatment exhibits contractions formed on the inner wall 11 and/or the outer wall 12, which may lead to the development of some structural defects and thus to a breakage of the pipe. Further, the through-holes cannot be completely closed by the proposed method, because the closing is performed only by contact bonding which is caused by deforming or crushing the pipe-wall. In addition, the operation required for rotating the mold 103 is very complicated.
In Japanese Published Unexamined Patent Application No. 54-103480 there is disclosed a method in which, as FIGS. 1 and 11(a) and (b) illustrate, hole-partition walls 130 of the pipe end 10 are broken by a cutting tool 104 while the pipe end is heated. Then the inner and outer walls 11, 12 are pressed by a pressing mold 105 to be contact-bonded together. However, in this method, the adhesion of the crushed portions is not satisfactory. This method also involves a number of stages and is complicated.
In both of the above two methods, the through-holes 13 are merely crushed by pressing. This involves a high possibility that the once-closed portion may be reopened when the pipe is subjected to secondary processing such as diametrical enlargement, after closing of the through-holes, or when any shock such as dropping, or any property change with time occurs. Also, in the case of resin pipes made of polyvinyl chloride, which has a melting temperature and a decomposition temperature in close proximity to each other, are to be connected with each other, the heating temperature and heating time must be strictly controlled, and, therefore, the operation is very complicated.
Besides the above mentioned methods, there is a known method in which a caulking material such as a silicone resin, is injected into the through-holes 13 to plug or close them. However, the injection of such caulking material into individual through-holes is quite troublesome. Such a method of closing the holes naturally involves variations in sealing performance among the through-holes. Furthermore, the silicone resin and polyvinyl chloride are incompatible with each other. Therefore, this third method does not assure a satisfactory closing effect.
It has been also proposed to attach a blind plate made of a resilient material to the wall-end of the resin pipe 1. However, such a blind plate may be easily detached from the end by applying only a small force. Therefore, this method is not a satisfactory one.